THE STORY OF OUR ROCK FOUNDATION 



A1 



Figs. 30-33. — Fig. 30. — Map showing land and sea when the Potsdam sand- 

 stone was depositing (Upper Acadian). Fig. 31. — When Magnesian limestone 

 was depositing (Beekmantown). Fig. 32. — When Richmond shales were depositing 

 (Cincinnatian). Fig. 2>3- — When part of the Niagara limestone was depositing 

 (Mid-Silurian). Land is white, sea finely lined; black shows areas of present 

 outcrop. All after Schuchert. 



